Torque control method for drive system of electric vehicle

Abstract

In a torque control method for a drive system of an electric vehicle configured for generating torque by evading a backlash band to prevent occurrence of backlash in the drive system, torque control modes include a contra-directional distribution mode in an acceleration direction in which a front-wheel torque command is determined to be a maximum front-wheel torque threshold value set as a negative (−) torque value in a regenerative direction and a rear-wheel torque command is determined to be a positive (+) torque value in a driving direction and a contra-directional distribution mode in a regenerative direction in which the rear-wheel torque command is determined to be a minimum rear-wheel torque threshold value set as a positive (+) torque value in the driving direction and the front-wheel torque command is determined to be a negative (−) torque value in the regenerative direction thereof.

What is claimed is: 
     
       1. A method of controlling torque of a drive system of a vehicle, the method comprising:
 determining, by a controller, a total torque command required for driving of the vehicle; 
 determining, by the controller, a torque control mode corresponding to a current driving state of the vehicle among a plurality of preset torque control modes and entering the determined torque control mode; 
 determining, by the controller, a front-wheel torque command and a rear-wheel torque command according to the entered torque control mode from the determined total torque command; and 
 controlling, by the controller, a front-wheel motor and a rear-wheel motor of the vehicle in response to the determined front-wheel torque command and the determined rear-wheel torque command, 
 wherein the plurality of torque control modes includes:
 a contra-directional distribution mode in an acceleration direction in which the front-wheel torque command is determined to be a maximum front-wheel torque threshold value set as a negative (−) torque value in a regenerative direction and the rear-wheel torque command is determined to be a positive (+) torque value in a driving direction; and 
 a contra-directional distribution mode in a regenerative direction in which the rear-wheel torque command is determined to be a minimum rear-wheel torque threshold value set as a positive (+) torque value in the driving direction and the front-wheel torque command is determined to be a negative (−) torque value in the regenerative direction. 
 
 
     
     
       2. The method of  claim 1 ,
 wherein, in the contra-directional distribution mode in the acceleration direction, the rear-wheel torque command is determined to be a value obtained by subtracting the maximum front-wheel torque threshold value from the total torque command, and 
 wherein, in the contra-directional distribution mode in the regenerative direction, the front-wheel torque command is determined to be a value obtained by subtracting the minimum rear-wheel torque threshold value from the total torque command. 
 
     
     
       3. The method of  claim 1 ,
 wherein the maximum front-wheel torque threshold value is set to a value smaller than a lower limit threshold value of a backlash band set as a torque region including a possibility of occurrence of backlash in a front-wheel-side drive system, and 
 wherein the minimum rear-wheel torque threshold value is set to a value greater than an upper limit threshold value of a backlash band set as a torque region including a possibility of occurrence of backlash in a rear-wheel-side drive system. 
 
     
     
       4. The method of  claim 1 , wherein, in the determining of the torque control mode and the entering of the determined torque control mode,
 in response that the current driving state of the vehicle is an off state in which an accelerator pedal and a brake pedal are released, the contra-directional distribution mode in the regenerative direction is determined, and 
 in response that the current driving state of the vehicle is an accelerator pedal on state in which the accelerator pedal is applied and in response that the total torque command is equal to or less than a predetermined mode switching threshold value, the contra-directional distribution mode in the acceleration direction is determined. 
 
     
     
       5. The method of  claim 4 , wherein, in the determining of the torque control mode and the entering of the determined torque control mode,
 in response that the accelerator pedal on state is entered and the total torque command becomes equal to or less than the mode switching threshold value during the contra-directional distribution mode in the regenerative direction, the contra-directional distribution mode in the acceleration direction is entered. 
 
     
     
       6. The method of  claim 4 , wherein, in the determining of the torque control mode and the entering of the determined torque control mode,
 in response that the accelerator pedal and the brake pedal are turned off during the contra-directional distribution mode in the acceleration direction, the contra-directional distribution mode in the regenerative direction is entered. 
 
     
     
       7. The method of  claim 1 , wherein the plurality of torque control modes further includes a co-directional distribution mode in an acceleration direction in which the front-wheel torque command and the rear-wheel torque command are determined to be positive (+) torque values. 
     
     
       8. The method of  claim 7 , wherein, in the determining of the torque control mode and the entering of the determined torque control mode,
 in response that the current driving state of the vehicle is an accelerator pedal on state in which an accelerator pedal is applied and in response that the total torque command exceeds a predetermined mode switching threshold value, the co-directional distribution mode in the acceleration direction is determined. 
 
     
     
       9. The method of  claim 8 , wherein, in the determining of the torque control mode and the entering of the determined torque control mode,
 in response that the accelerator pedal on state is entered and the total torque command exceeds the mode switching threshold value during the contra-directional distribution mode in the acceleration direction, the co-directional distribution mode in the acceleration direction is entered. 
 
     
     
       10. The method of  claim 9 , wherein, in response that the torque control mode is switched from the contra-directional distribution mode in the acceleration direction to the co-directional distribution mode in the acceleration direction, while the front-wheel torque command is changed to pass through a backlash band set as a torque region including 0 torque, the controller is further configured to perform slope limiting to limit a slope of the front-wheel torque command to a predetermined maximum allowable change rate, and to determine a value obtained by subtracting the front-wheel torque command including the limited slope from the total torque command to be the rear-wheel torque command. 
     
     
       11. The method of  claim 9 , wherein, in response that the torque control mode is switched from the co-directional distribution mode in the acceleration direction to the contra-directional distribution mode in the acceleration direction, while the front-wheel torque command is changed to pass through a backlash band set as a torque region including 0 torque, the controller is further configured to perform slope limiting to limit a slope of the front-wheel torque command to a predetermined maximum allowable change rate, and to determine a value obtained by subtracting the front-wheel torque command including the limited slope from the total torque command to be the rear-wheel torque command. 
     
     
       12. The method of  claim 9 , wherein, in response that the torque control mode is switched from the co-directional distribution mode in the acceleration direction to the contra-directional distribution mode in the acceleration direction, while the front-wheel torque command is changed to pass through a backlash band set as a torque region including 0 torque, the controller is further configured to perform slope limiting to limit a slope of the front-wheel torque command to a predetermined maximum allowable change rate, and
 wherein, in response that a value obtained by subtracting the front-wheel torque command including the limited slope from the total torque command is equal to or less than the minimum rear-wheel torque threshold value, the controller is further configured to determine the minimum rear-wheel torque threshold value to be the rear-wheel torque command, and to generate a friction braking torque command corresponding to a value obtained by subtracting the front-wheel torque command including the limited slope and the minimum rear-wheel torque threshold value from the total torque command and to generate friction braking torque using a friction braking device. 
 
     
     
       13. The method of  claim 1 , wherein the plurality of torque control modes further includes a co-directional distribution mode in a regenerative direction in which the front-wheel torque command and the rear-wheel torque command are determined to be negative (−) torque values. 
     
     
       14. The method of  claim 13 , wherein, in the determining of the torque control mode and the entering of the determined torque control mode,
 in response that the current driving state of the vehicle is a brake pedal on state in which a brake pedal is applied, the co-directional distribution mode in the regenerative direction is determined. 
 
     
     
       15. The method of  claim 14 , wherein, in the determining of the torque control mode and the entering of the determined torque control mode,
 in response that the brake pedal on state is entered during the contra-directional distribution mode in the regenerative direction, the co-directional distribution mode in the regenerative direction is entered. 
 
     
     
       16. The method of  claim 15 , wherein, in response that the torque control mode is switched from the contra-directional distribution mode in the regenerative direction to the co-directional distribution mode in the regenerative direction, while the rear-wheel torque command is changed to pass through a backlash band set as a torque region including 0 torque, the controller is further configured to perform slope limiting to limit a slope of the rear-wheel torque command to a predetermined maximum allowable change rate, and to determine a maximum value among a value obtained by subtracting the rear-wheel torque command including the limited slope from the total torque command and a lower limit value of torque of the front-wheel motor to be the front-wheel torque command. 
     
     
       17. The method of  claim 16 , wherein, in response that the torque control mode is switched from the contra-directional distribution mode in the regenerative direction to the co-directional distribution mode in the regenerative direction, while the rear-wheel torque command is changed to pass through the backlash band, the controller is further configured to generate a friction braking torque command corresponding to a value obtained by subtracting the rear-wheel torque command including the limited slope and the front-wheel torque command from the total torque command and to generate friction braking torque using a friction braking device upon determining the lower limit value of torque of the front-wheel motor to be the front-wheel torque command. 
     
     
       18. The method of  claim 15 , wherein, in response that the torque control mode is switched from the co-directional distribution mode in the regenerative direction to the contra-directional distribution mode in the regenerative direction, while the rear-wheel torque command is changed to pass through a backlash band set as a torque region including 0 torque, the controller is further configured to perform slope limiting to limit a slope of the rear-wheel torque command to a predetermined maximum allowable change rate, and to determine a value obtained by subtracting the rear-wheel torque command including the limited slope from the total torque command to be the front-wheel torque command. 
     
     
       19. The method of  claim 14 , wherein, in the determining of the front-wheel torque command and the rear-wheel torque command, the front-wheel torque command and the rear-wheel torque command are determined to generate regenerative braking torque through a front/rear wheel torque distribution process of distributing the total torque command according to a front/rear wheel distribution ratio during the co-directional distribution mode in the regenerative direction thereof. 
     
     
       20. The method of  claim 19 , wherein, in response that a sum of the front-wheel torque command and the rear-wheel torque command does not satisfy the total torque command due to a lower limit of torque of the front-wheel motor or the rear-wheel motor during the co-directional distribution mode in the regenerative direction, the controller is further configured to generate friction braking torque using a friction braking device so that a sum of the regenerative braking torque generated by the front-wheel torque command and the rear-wheel torque command and the generated friction braking torque satisfies braking torque of the total torque command.